Date: Tue, 6 May 2003 18:13:48 +0400 (MSD) From: Igor Sysoev <is@rambler-co.ru> To: Terry Lambert <tlambert2@mindspring.com> Cc: freebsd-arch@freebsd.org Subject: Re: rfork(RFPROC|RFMEM) Message-ID: <Pine.BSF.4.21.0305061751340.64470-100000@is> In-Reply-To: <3EB72C95.6E9EEA50@mindspring.com>
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On Mon, 5 May 2003, Terry Lambert wrote:
> Igor Sysoev wrote:
> > On Mon, 5 May 2003, Terry Lambert wrote:
> > What is stack glue ?
>
> See the code in fork1() in /sys/kern/kern_fork.c.
I do not see any stack manipulation in kern_fork.c except the creating
alternate kstack for KSE thread in 5.0. And rfork(2) can not create
such stack - it passes 0 to fork1().
In 4.x there's no stack code at all.
> > I use rfork_thread(3) wrapper that allows to setup another stack for
> > rfork()ed process.
By the way I found the bug in x86 rfork_thread(3)'s error handling:
--- /usr/src/lib/libc/i386/gen/rfork_thread.S Wed Feb 7 03:12:45 2001
+++ /usr/src/lib/libc/i386/gen/rfork_thread.S Tue May 6 17:45:14 2003
@@ -108,5 +108,8 @@
* Branch here if the thread creation fails:
*/
2:
+ popl %esi
+ movl %ebp, %esp
+ popl %ebp
PIC_PROLOGUE
jmp PIC_PLT(HIDENAME(cerror))
> > What RFTHREAD flag does ?
>
> See the code. It basically sets up for kernel threading, rather
> than merely for processes sharing the same address space and/or
> file descriptor table and/or heap, which is what rfork was
> intended to be able to do. It also ensures propagation of any
> SIGKILL to all peers, so they die all at once, in exit1() in
> /sys/kern/kern_exit.c.
It seems that the single purpose of the RFTHREAD flag is to kill peers
when the leader got SIGKILL.
And in 4.8-STABLE and 5.0-CURRENT (after 5.0-RELEASE) the leader also
holds P_ADVLOCK flag.
> > By the way linuxthreads port always uses RFTHREAD flag.
>
> They don't know any other way than the moral equivalent of
> the Linux "clone" system call, so that's what they use; it's
> technically not necessary. See also the source code in the
Now it's necessary. Otherwise rfork() returns EINVAL.
> directory /usr/src/lib/libpthread, which doesn't use rfork()
> at all.
I know it.
Igor Sysoev
http://sysoev.ru/en/
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